I'm headed to Laos and Cambodia and I'm worried about the side effects of the Malarone anti-malaria medication. Is it necessary to take this? What is the likelihood of transmission of malaria in this country? I know this is not a high risk.
Actually if you look at the CDC (Center for Disease Control) website pages for Laos and Cambodia, Doxycycline is also recommended, if you wish to avoid taking Atovaquone-proguanil (Malarone). Something you should discuss & decide with your doctor not with strangers.
The other option adopted by many (especially if you are hanging out in bigger cities, not trekking in the jungle) is simply avoid being bitten by mosquitoes by using long clothes and/or repellents.
Of course time of year comes into play as well. Right now we are heading towards the end of the winter dry season, no rain for many months, hence mosquito population have been drastically reduced (but never totally gone). Thus lower risk to an already low risk. But when the rains return so do the mosquitoes.
But an even bigger consideration is that there are three nasty mosquito borne illness present in SE Asia: Malaria, Japanese Encephalitis and Dengue. The first two have preventative courses of action, Dengue does not. So the "avoid being bitten by mosquitoes" course of action comes into play no matter what you choose for the other two. Might as well use it for all three.
CDC malaria pages: