Your beer may have a medicine taste because of these reasons listed below;

Most likely caused by chlorophenols - These taste like

• disinfectant
• cough syrup
• mouthwash
• Band-Aid™
• smoke
• clove-like (spicy)
• plastic
• vinyl
• iodine

Chlorophenols are commonly caused by:

• Use of chlorinated water during brewing - Chlorine and chloramines are added to the municipal water supply to kill microorganisms in the water between the water treatment plant and the home. The concentrations that are included in the water are harmless to humans. However, these concentrations are harmful to yeast and when the yeast metabolises the chlorine and chloramines the yeast produces chlorophenols which can be perceived as the tastes listed above. Fix this by;
  1. Brewing with carbon filtered water, to boil your municipal water for 7 minutes before use,
  2. Use Camden tablets to remove the chlorine and chloramines or if your municipal water only contains chlorine then you can let the water stand for 3 hours before brewing.
• Infection of wild yeast and bacteria - Starsan or Total San is a gram-negative killer which means they are very good at killing organisms which can do you harm like E. Coli. However, many yeast and bacterial cells are gram-positive which these are less effective against. These wild yeasts and bacteria are more likely to produce off flavours including many esters and phenols that may have a medicinal taste. Fix this by;
  1. Minimise exposure of the wort/beer to air at all stages
  2. Clean equipment
  3. If still an issue, double sanitise with an alkaline sanitiser and an acidic sanitiser
• Over-extraction of the hops - When dry hopping beer, you are adding a substantial amount of plant matter to the beer. This is done so that the oils in the hops can be extracted to give flavour and aroma. However, there is a lot of chlorophyll in the plants (which gives them their green colour) which, when the hops are in the beer for an extended period of time (over a week), can be extracted and will give a vegetal, medical or chlorophyll taste to the beer.