Don't apply Minoxidil solution (Trugain) on skin where you also use Tretinoin. Tretinoin changes the skin's outer protective layer, which can make the skin absorb more Minoxidil than usual. Dithranol has the same effect. If you use both, ask your doctor or pharmacist how to manage them.
These medicines can affect each other in a serious way. Do not start taking them together unless your doctor has said it is OK. If you already take both, do not stop either one on your own: speak to your doctor or pharmacist soon.
What to do: Do not use these together on the same skin area unless your doctor has said so. Ask your doctor or pharmacist how to manage them.