Sweetsleep

Sweetsleep has numerous properties similar to barbiturates - notably use in small doses as an anti-anxiety and anti-convulsant, higher doses to induce sleep, and even higher doses to kill (they are commonly used this way by veterinarians for euthanasia, they are also used in cases of physician assisted suicide and death penalty by lethal injection).

Benzodiazepines (Valium, Xanax, etc.) have similar effects (and operate on the same neuroreceptors) and have largely replaced barbiturate use medically as overdoses are rarely fatal. However, they are also known to sometimes cause nose-bleeds (one of the things Maester Coleman was asking Sansa about Robert Arryn).

I'm not familiar with the effects of long-term barbiturate use, but there is a lot of information available on long term Benzodiazepine use. Much of it is psychological, and would make for some great roleplay material: irritability, increased pain levels, increased anxiety, insomnia, and (possibly) impulsiveness and violent outbursts. Another key one is cognitive impairment; insufficient to affect daily life, but impairs more cognitively demanding tasks.

In both, tolerance to the medicinal benefits tends to increase faster than the tolerance to the side effects; this leads to larger doses being needed, increasing the likelihood of overdose or side effects. This could be the sort of thing Maester Coleman was concerned about regarding Robert Arryn.

I did not expect my knowledge of psychopharmaceuticals to be relevant in this game.