There are three antimalarials that are effective in Colombia. Atovaquone/proguanil (Malarone, Malanil); mefloquine (Lariam, Mefiam, Tropicur); and doxycycline (Vibramycin & many other brands). The stories you have heard about side effects may have been about mefloquine.
Malarone has few reported side effects. Generally, fewer than 5 % of users have reported problems (in research studies, the same percentage as people taking a useless sugar pill that they thought was Malarone). The most common reported problems are stomach ache, nausea, and headache.
One thing that a lot of people don't know about Malarone is that for maximum effectiveness, it needs to be taken with something with fat in it, as fat helps you absorb the ingredients. Coffee with milker cream. A meal cooked with oil. Buttered toast. A gooey dessert.
Yes, there is risk of malaria in Riohacha. In fact, there is risk pretty much anywhere in Colombia below 1700 meters. One thing you need to consider--and only you & your doctor can do this--is whether you have some medical condition that mens that if you got malaria, it would be unusually serious.
Although it doesn't happen a lot in healthy adults, malaria can be rapidly fatal, sometimes within hours of the appearance of symptoms.
As for gin & tonic (yeas, I know you are just having fun here)--Gin & tonic is often jokingly recommended to prevent malaria, because tonic has (or used to have) the anti-malarial quinine in it.
Alas, the amount of quinine in tonic is pretty minuscule. If you look at the fine print on the bottle, you'll often find that it is contains "quinine flavor," not quinine itself.
Some people with too much time on their hands calculated how much tonic you would need to drink to prevent malaria--estimates range from 5 to 67 (!) liters a day. If you consume that as gin & tonic, as Uncle Cecil from the Straight Dope notes, malaria may well be the least of your problems.
