i've written before on this, but here we go again...
http://en.wikipedia.org/wiki/Viagra
this drug is sildenafil citrate. the Wiki entry explains origins and side-effects well and is worth reading. but its information on patents is vague. Wikipedia used to list all the Indian versions of SC but Big Pharma has more lawyers, it seems.
SC is produced by pharmaceutical plants in several Indian locations and packaged for retail sale under brand names such as Kamagra and Veetab. distribution is not straightforward as many countries have signed treaties promising they will adhere to US patent-law. in such regions (which include HK and Thailand), pharmacies won't have the Indian products stocked on the shelves. they may informally sell Viagra, which may or may not be genuine.
the OP asked about Cialis (tadalafil,
http://en.wikipedia.org/wiki/Cialis)--the situation is similar, with the Indian version called "Apcalis", with similar packaging. there may be other Indian-made products, but these have also been scrubbed from Wikipedia.
i've used Veetab, Kamagra and Seagra--all made in India and purchased in Phnom Penh. they are professionally made and packaged, far cheaper than Pfizer's version and work well. but, as ever, anyone considering the use of an enzyme-inhibitor to enhance erections should consult their doctor. side-effects do occur--while they're generally mild, there are interactions with drugs such as nitrates which can be serious. ask your doctor.
i have no opinion on online sales as i get my supply in Phnom Penh, from an air-conditioned pharmacy with a choice of brands and clearly printed manufacture/expiration dates, and keep it in a controlled environment (that would be my refrigerator, also a good place to store condoms as heat degrades latex over time).
FUN FACTS:
"In the United States, the FDA relaxed rules on prescription drug marketing in 1997, allowing advertisements targeted directly to consumers...Stuart Elliot of The New York Times opined: "The continuous presence of women in Cialis ads is a subtle signal that the drug makes it easier for them to set the pace with their men, in contrast to the primarily male-driven imagery for Levitra and Viagra."
"Tadalafil, sildenafil, and vardenafil all act by inhibiting the PDE5 enzyme. These drugs also inhibit other PDE enzymes. Sildenafil and vardenafil inhibit PDE6, an enzyme found in the eye, more than tadalafil. Some sildenafil users see a bluish tinge and have a heightened sensitivity to light because of PDE6 inhibition."
JtB
PS: an extensive list of SC generics appears here:
http://www.igenericdrugs.com/?s=Veetab¬ran=&showfull=1
it seems a worldwide phenomenon...some of the brand names are hilarious. i would stick with the Indian varieties, which list the address of the manufacturer on the box.
true story: i was looking behind the mini-fridge in my Phnom Penh hotel room one day (the outlet there stays on when room-key is removed, so it's the place to plug in a device to charge when you're out of the room) and found a four-tablet blister-pack of Chinese-made SC. there was no English writing whatsoever, but the image of a howling wolf and the classic blue-lozenge shape (not to mention WHERE i found it) made it obvious that this was SC. what the hell. i figured they were 100mg, cut it to the appropriate dosage and took some.
worked like a charm
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Last edited by JackTheBat at 22-7-2012 10:52 ]