Final answer:
Common OTC medicines that interact with lithium include ibuprofen, diuretics, and some cough and cold medications with decongestants.
Step-by-step explanation:
One common OTC medicine that interacts with lithium is ibuprofen, which is a nonsteroidal anti-inflammatory drug (NSAID). Taking ibuprofen with lithium can increase the levels of lithium in the blood, potentially leading to lithium toxicity. It is important to consult a healthcare professional before taking any OTC medications while on lithium.
Another OTC medicine that may interact with lithium is diuretics. Diuretics like furosemide can decrease the excretion of lithium, increasing its levels in the blood.
Additionally, some cough and cold medications that contain decongestants like pseudoephedrine can also interact with lithium and may worsen its side effects.