The duration of time required for this medication to start clearing a fungal infection depends on the location of the infection. Individuals with fungal skin infection usually begin to see the infection starting to clear within 2 weeks of starting Grifulvin. Around 4 weeks will be required for fungal scalp infections or in the hair. Foot infections will also require approximately 4 weeks, and fingernail or toenail fungal infections can take up to months for this medication to overcome them completely.