1)  Through  Astrological works, the benefic nature of Jupiter is well known. Even  some of my colleague astrologers have referred to Jupiter as the only  benefic planet while Venus, the Moon and Mercury have been given  secondary position. However, in practice, Jupiter has proved to be  malefic in certain situations, i.e. by placement, association, aspect,  the ding in which it is placed and by whom is being aspected. In this  write-up, instances shall be referred to the situations where Jupiter  has proved to be a malefic.
2)  To start with, knowledge of  a little background about Jupiter and its benefic nature is necessary.  In general, Jupiter denotes government i.e. represents officials, who  give advice to the government. Jupiter gives all comforts of life and  related amenities, benefic aspect of the Jupiter can turn the table  where otherwise bad results may be expected. Jupiter represents the highest class of  society including priests and teachers. Jupiter is competent to give  male issues. He makes the native well-versed in all branches of  knowledge. He also gives wealth. Normally it has been seen that during  major period of Jupiter, the native engages himself in religious and  sacred duties, gets promotion if in government service  and reaches higher strata if in business. The native firmly believes in  God, has all comforts of riches, gold, clothes. Conveyances, wife and  son(s), may be recognized as chief among his community and above all is  endowed with acts of high spiritual nature.
3)  Briefly,  it can be summed up that the Jupiter is known to be signification of  children, wealth, education, name, fame, prosperity and happy married  life. Jupiter gives the native political power, finances and good luck.  The native will be known for his good qualities, prosperous and a  charming personality. Persons engaged as judges, magistrates etc need  strong Jupiter. Jupiter is the planet that has a big hand in making the  native an eloquent speaker, most imaginative and also writer or author.  He enables the native to enjoy Raja Yoga if in an angle, tine or in the  11th house occupying own or exalted sign.
4)   Jupiter is the next in orbit to Saturn. He takes roughly 12 years to complete a cycle of the zodiac but exactly the period is eleven years, three hundred and fourteen days, twelve hours, twenty minutes and nine seconds.
Known  for great fortune as stated above, Jupiter is considered to be a hot,  moist, airy, sanguine, masculine, and social planet. Jupiter has been  described to be well dignified and thus makes the natives born under his  influence wise, magnanimous, jovial, just, mild-mannered with moderate  temperament and inclined to religious matters. Jupiter increases the  chances of success in all fields and adds to the executive ability of  the native. It has been recognized by all that the Jupiter is the symbol  of wisdom and is the largest planet of our solar system. At the same  time as Marker a (Killer). Jupiter would cause death without much  trouble or through phlegmatic disorders.
5)  Out of the 12 signs (Rasis), Jupiter owns two signs: Sagittarius and Pisces: Persons born under Sagittarius have been described to be incurably optimistic. Sagittarius  is a dual sign. Sagittarians always strive for better things. By and  large, they have been found to be little restless and at the same time  they do not want to put themselves in danger of bodily peril. It has  however been seen that more octogenarians are born under this sign of  Jupiter. They have great resave force of energy but they do spend more  energy in daily life with little tendency to economies energy, but their  love of environments and outdoor life is supreme though accidental  troubles cannot be ruled out-accidents to hips, hands or hips and also  suffering from rheumatism and through government. With ideal vision,  their general temperament is calm and cheerful.
6)   Jupiter  has been said to be of long stature. The aspect of Jupiter makes one  little taller as Mercury, Saturn and Rahu are expected to do Jupiter in  Lagna is stated to be endowed with directional strength. 
Jupiter has been said to be signification of wealth. If Venus is placed in the 12th  house form Jupiter and Jupiter has good lordships too in the horoscope,  the native is bound to be rich. The richness would depend on the  position of other planets also and dasa periods during which richness  would accrue.
In one of the cases 6th  house Jupiter with the moon (Aries Lagna having Saturn) failed to save  the native from skin trouble (leprosy) though Mercury happened to be in  own sign Gemini with the Sun. other planets being- Venus and Rahu in the  2nd house, Mars in the 4th and Ketu in the 8th house.
7)  In Zodiac, Sagittarius  is the first sign owned by Jupiter followed by Pisces. Jupiter in its  own sign normally is said to make the native sincere, fortunate,  successful and enterprising. Such natives have been found to gain after  marriage. Depending on the combinations it can be a case of one marriage  and many affairs. Such persons have been advised to curtain speculative  tendencies as the are likely to suffer losses (NO game of chance for  persons born under sign of Sagittarius though they can gain from the games of mind).
Sagittarius persons are capable of foreseeing the outcome  of a transaction from its inception. Frank, open-hearted, and truthful,  such persons get distressed with small annoyances. Generally, it has  been that Sagittarius persons are clam and cheerful but they also get  excited beyond control at times. So to say extraordinary mental activity  is the chide characteristic of Sagittarius native. Normally, such  natives become teachers, preachers and also exponents of law and that is  why legal profession is said to be an excellent field for them. They  are fond of arguments and enjoy cross words with finer sense of humor.
Unless  Jupiter is badly afflicted, such natives are financially well equipped.  This would depend on how Jupiter is aspected by malefic and the  strength of Jupiter including his degree at the rising time. Be that as  it may, a well developed Sagittarius, i.e. with many good planets in own  houses, friendly houses, in exalted positions, produces a commanding  figure in the financial world.
One of the bad things noted about Sagittarius  persons is that they make promises but forget. However, such persons  are tactful in having malefic influence in their horoscopes may prove to  be spiteful. Therefore, such persons do acquire the likings of their  subordinates but never command their affection.
8)  Pisces  (Meena): this is another sign owned by Jupiter. This is a watery and  dual sign. Natives born under this sign are liable to incur various  diseases but they recover speedily. In normal health, they have been  seen to exhibit wonderful vitality. Pisces natives normally come under  fluency of some toxins or drugs. Some natives have deep interest in  religious matters and art. With negative character, Pisces natives have  no power of discrimination and have no capacity to resist any set of  thoughts. However, the adoptability of native to circumstances is his  best guarantee of survival. Strong planets in his ascendant of survival.  Strong planets in the ascendant or powerful aspects of  Jupiter. With regard to spiritual approach, Pisces people have been  found to respond to the matters of soul apart form earthly matters. Such  natives confuse material and spiritual planes. Alcohol has been found  to be extremely bad for these natives.
Regarding finances, Pisces native have been noted to be careless and like to spend profusely with little judgment. They may be generous at times but not wise. Socially, such natives are inclined to see everything  through rose colored spectacles. In love matters, devotion may exceed  that of Taurus natives. Women with this sign rising are usually  beautiful and fertile. Pisces women make an ideal wife. With these  general narrations, it would be apt to say that a detailed delineation  of personal horoscope of the native may reveal the truth.
9)       
a. When  Jupiter occupies Sagittarius or Pisces (own sings) or Cancer (sign of  exaltation) identical with Kendra, Hamsa Yoga will be king, high  political or government dignitary respected by people. Such persons are  said to be virtuous. But this is not normally seen and we need  verification of certain horoscopes. Again, it would depend on the  combination in the horoscope and role of malefic.
b. With  Jupiter in own sign Sagittarius or Pisces, as the Lagan, the native may  be bilious and phlegmatic and may suffer from tumors. Such Jupiter  makes some natives, of course, depending on their personal horoscopes,  issueless, ungrateful, vain and hostile.
c.  Jupiter of Sagittarius or Pisces makes the native inferiors in company; his enemies also rise if Jupiter is in 3rd house. He may also hate his sons and friends.
d.  Jupiter in 5th  house, if in Sagittarius-children will be born with great difficulty.  If Jupiter is in Pieces, children may be short-lived. If Jupiter happens  to be in masculine sign, denial of children may be short-lived. If  Jupiter happens to be in masculine sign, denial of children may be  short-lived. If Jupiter happens to be in masculine sign, denial of  children, few children or sick children are possible.
e.  With Jupiter in 8th house, pangs of death may be unbearable.
f.   Among  other things, Varaha Minhira in his Brihat Jataka has said that persons  with Sagittarius Lagan (ruled by the most benefic Jupiter) have been  found to be fond of murdering brothers and are not inclined to charity.  They quarrel with wife, suffer from facial diseases and die by  quadrupeds, serpents and imprisonment. And, persons under the other sign  of Jupiter i.e. Pisces, have capricious mind and have many enemies,  death is indicated by diseases in sexual organ, or while traveling.
10)   
a.  The accepted canons of astrology are that the Jupiter stands for and is concerned with the following matters.
Knowledge,  noble qualities, impairing knowledge, sons (progeny), minister,  counselors, good behaviors, magnanimity, mastership over sense,  knowledge of Sruits, Sastras, Smritis, progress in every direction,  beauty, devotion towards Gods and Brahmins, religious faith, sacrifice,  penance, honor, kindness, sympathy, magnanimity happiness of the  husband, signification of the husband in females horoscopes, learning in  Vedas, Sastras, Smritis and sacred lore, philosophy astrology,  Brahmins, sages and ascetics, auspiciousness, virtue, physical  toughness, gold, bed, conveyance, position and also residence.
Jupiter  also signifies husband in the case of female natives. Now the question  arises when the Jupiter himself becomes the lord of the 7th  house, would it always give cordial relations and long life to the  husband. It is not always true and in the case of female natives also,  if Jupiter comes under the influence of Separative planets – the Sun,  Saturn and Rahu in life, separation plants – the Sun, Saturn and Rahu in  life, separation and diverse are bound to come under malefic dasa.
 
