Viagra, Kamagra contain an effective medicinal substance for the treatment of erectile dysfunction. The drug is approved by the state. Only an authorised person (e.g. a pharmacy) may sell the medicine.
Preparations with an active substance are considered a medicinal product under the Medicines Act (section 2(1)(b) of Act 387/2007Sb). The medicinal product must be registered as a medicinal product in the country concerned. Only after registration can it be offered to the public. This applies to Viagra but not to Kamagra and many generic erectile dysfunction medicines. Unapproved drugs cannot be offered at all. Not even by authorised persons, e.g. doctors or pharmacists.
From the report According to the declaration of the State Institute for Drug Control of the Czech Republic, "The preparations Kamagra 100 mg and Sildenafil citrate 100 mg contain the active substance sildenafil 100 mg/tbl... The preparations Tadalis SX 20 mg and Tadalafil 20mg contain the active substance tadalafil 20 mg/tbl. All of the above products are unregistered in the Czech Republic and meet the definition of a medicinal product based on their composition. "
Even if the drugs are approved by the state, sex shops are certified to sell them. We don't even have Kamagra as an under-the-counter item.
Kamagra could previously be obtained directly from India through the auction portal ebay.com. Now you are more likely to find Viagra or other products with the active ingredient sildenafil on eBay. However, it is always better to consult a doctor beforehand. For people with heart problems, erectile dysfunction drugs can be dangerous. Occasionally, some lunatic throws it up on the auction block :).
Other erection support products sold in sex shops are without an effective therapeutic agent. These are dietary supplements.