Hi @JimInBC, the thinking behind the allowables is that when one only eats one meal a day, they can get a little hungry in the evening and their sugar levels drop, they can feel tired and sometimes have hunger pains, which can make it difficult to practice. So the Buddha allowed tonics in the evenings.
Here at Lokanta Vihara we have only one meal, and rarely have any tonics. We rely on juice for sugar a sugar hit. You get used to it after some time.
Here’s a good summary from Bhante Ariyesako’s book on the Bhikkkhus Rules for Laypeople.
MEDICINES OR TONICS
We have dealt above with food and fruit juice. There is now the category of ‘tonic-medicines’ (sattaahakaalika). These can be consumed at any time but cannot be stored longer than seven days (after they are offered).
These tonic-medicines were originally regulated when Venerable Pilindavaccha’s great feats of psychic power made him so famous that he received many offerings of the five ‘tonics.’ Even though he distributed these among other monks there was so much that the excess had to be stored away and their dwellings were overrun by rats. Visiting lay people criticized the monks for “storing up goods in abundance like a king.” The Buddha therefore set down this rule:
"Keeping any of the five tonics — ghee, fresh butter, oil, honey, or sugar/molasses — for more than seven days is [an offence of Confession with Forfeiture.] (Summarized Nis. Paac. 23; BMC p.242)
◊ There are various translations and interpretations about these ‘tonic- medicines’ — according to different Communities and different countries. Some places consider only liquids allowable while a few communities will drink only plain water in the afternoon. Some communities will not accept re-offered tonic-medicines (after the seven days period is over), some will under certain circumstances. Therefore lay devotees need to enquire about the practice of their local Community and follow that way.
Some contemporary observations:
“The five medicines — ghee, navaniita.m, oil, honey, and suga — were allowed by the Buddha to be consumed by ‘sick’ monks at any time of the day or night. According to the Mahaavagga, these five were ‘agreed upon as medicines and, although they served as nutriment for people, were not considered as substantial food.’ The degree of infirmity required before a monk is allowed to consume these [tonic-]medicines is a controversial point… It seems that feeling rundown or feeling tired after physical exertion would be sufficient cause to be able to make use of the Five Medicines.”(AB)
“The main effectiveness of these medicines seems to be in their nutritional value. They do not have medicinal value as commonly understood today, for example, relieving pain or as an antiseptic. However, as nutriment they would help to maintain bodily strength and assist in recuperation while, since they are so rich, would not be a substitute for normal food.” (HS ch.10)
Also, if the tonic-medicine is mixed with a tiny amount of food then it would be acceptable according to this allowance:
“…if sugar has a little flour mixed with it simply to make it firmer — as sometimes happens in sugar cubes and blocks of palm sugar — it is still classed as a tonic as it is still regarded simply as ‘sugar.’” (BMC p.238-9)
If the flour is for more food-like reasons then it would be counted as food. See also Mixing Edibles above.
The fourth category of edibles (see The Four Sorts of Edibles) is that of Lifetime Medicines (yaavajiivika). which includes what we generally think of as medicines.
The basic principle set down by the Buddha about all medicines is in this reflection:
“Properly considering medicinal requisites for curing the sick, I use them: simply to ward off any pains of illness that have arisen, and for the maximum freedom from disease.” [OP p. 47; (Paali: M. I, 10; A. III, 387)]
In the beginning, the basic (herbal) medicines allowed by the Buddha were those pickled in urine. Later, nearly all other types came to be considered allowable. (See the separate allowance above for ‘tonic-medicines.’)
Medicines that may be consumed without time limitation are called yaavajiivika. The Texts mention different sorts of herbal medicines such as: plant roots, e.g., ginger, turmeric, sweet flag, etc.; decoctions, such as of the neem or nux-vomica; tree-leaves, such as neem-leaves, tulsi or holy basil; fruits, such as long peppers, myrobalan, wormwood; resins, such as asafoetida; salts, such as sea-salt, rock salt, etc. Any other medicine or herbs similar to these that is not reckoned to be food is included under this ‘lifetime’ category.
◊ Modern western medicines are usually included — using the Great Standards — under this category and therefore can be taken at any time of the day and kept as long as necessary.