star-lover,
Yes, many astrologers do see Neptune as signifying (or more technically, ruling) drugs and drug addiction. BUT, as you recognise, this is not the only thing that Neptune is associated with - others that have been advanced are;
dreams, inspiration, imagination, fantasy, sleep, the spiritual, the emphemeral, the obscure or hidden and musical ability.
Now, if we accept some or all of these then we have an issue of deciding which particular 'aspect' of Neptune we are looking at when reading a chart. Indeed this is an issue with any planet unless there is a clear context to to the interpretation such as a horary question.
It is dangerous to see Neptune in a chart and read that as only signifying drugs in some way. It is much more likely to be signifying something else.
serenaserendipity,
The reading of Jupiter in this way must be in the context of a decumbiture chart or a horary chart or an event chart where cancer is known or suspected. In the cases that I have met cancer has already been diagnosed and the chart relates to a horary question relating to the disease.
Cancer is an uncontrolled growth - and Jupiter is the planet of growth and expansion.
In one particular case of cancer the chart had Mercury in Pisces as ruler of the sixth house, and therefore the significator of the illness. Mercury was trine to Jupiter in Cancer in the sixth house. Mercury in Pisces is in both fall and detriment so the disease was particularly debilitating. Jupiter is exalted in Cancer so we have a very strong Jupiter which has an easy flow of energy to the ruler of the disease. The disease can easily grow and spread. As the aspect was applying the disease was progressing but not at its height. Luckily early treatment caught the cancer in time.
The context aids the interpretation - it was a chart relating to a diagnosis of cancer and in that context what you don't want to see is a propensity for the disease to grow easily and without obstruction.
Most introductory texts will state that Jupiter and Venus are benefics and Saturn and Mars are malefics but in context any planet can play the role of a benefic or alternatively play the role of a malefic.
