The potion of sickness is biologically contaminated fruit juice.
If you are a Healer then you are not subject to the following effects:
|blessed||You lose one hit point.|
|uncursed||You lose up to ten hit points, and one of your statistics is randomly reduced.|
|cursed||You lose up to fifteen hit points, and one of your statistics is randomly reduced.|
Additionally if you are hallucinating then you are shocked to your senses.
|"Yecch! This stuff tastes like poison."||You always receive this message.|
|"But in fact it was mildly stale [fruit; default is slime mold] juice.)"||The potion was blessed.|
|"(But in fact it was biologically contaminated [fruit; default is slime mold] juice.)"||The potion was not blessed, but you have poison resistance, so you only lost one point from one of your statistics.|
|"Fortunately, you have been immunized."||You are a Healer, so you suffer no ill-effects (hallucination is still cured).|
|"You are shocked back to your senses!"||You were hallucinating, and were cured by the potion.|
|"You feel weaker."||Your strength was lowered.|
|"Your muscles won't obey you."||Your dexterity was lowered.|
|"You feel very sick."||Your constitution was lowered.|
|"Your brain is on fire."||Your intelligence was lowered.|
|"Your judgement is impaired."||Your wisdom was lowered.|
|"You break out in hives."||Your charisma was lowered.|
However, if neither of those are available, dipping a missile weapon into a potion of sickness should form a coating on it.
You can #dip darts, arrows, shurikens and crossbow bolts into potion of sickness to coat the projectile weapon in poison. Poisoned weapons do d6 extra damage and have a 10% chance of instant kill for non-resistant monsters. However, the poison wears off 1/10 of the time. Unfortunately, in vanilla NetHack, this does not work on daggers, although it does in SLASH'EM.