Glycoalkaloids are a family of poisons commonly found in the plant species Solanum dulcamara (nightshade). There are several glycoalkaloids (alkaloids + sugars) that are potentially toxic. A prototypical glycoalkaloid is called solanine (sugar [solanose] + alkaloid [solanidine] = solanine), which is found in potatoes. The alkaloidal portion of the glycoalkaloid is also generically referred to as an aglycone. The intact glycoalkaloid is poorly absorbed from the GI tract but causes GI irritation. The aglycone is absorbed and is believed to be responsible for observed nervous system signs. Glycoalkaloids are bitter tasting, and produce a burning irritation in the back of the mouth and side of the tongue when eaten.
Laboratory diagnosis: although not routinely available, detection of alkaloids in tissues or urine is possible. 
Sale of a glycoalkaloid-based treatment marketed by Lane Labs USA Inc. for prevention of skin cancer was banned by the FDA in 2004 as an unapproved drug. Similar glycoalkaloid gels are now marketed as exfoliants.