Consult your doctor if you encounter any of these negative effects or have questions about using Viagra. Consult your healthcare practitioner for specific guidance if you are uncertain about the right dosage or timing. These include itraconazole Sporanox, Tolsura , ketoconazole Extina, Ketozole, others and ritonavir Norvir. Trying a Free Trial of Viagra Trying a free sample of Viagra before making a full purchase provides several benefits. When taking Viagra, stick to the directions and suggested dosage offered.The four main medicines taken by mouth for erectile dysfunction are: Avanafil (Stendra). Sildenafil (Viagra). Tadalafil (Cialis). Vardenafil. These medicines are called .  · 2. Rex MD – Free Viagra Samples. Rex MD is a men’s health-focused telemedicine service. They provide free prescription pharmaceutical samples for erectile .