Suzie, as they say, sola dosis facit venenum, or the dose makes the poison. Anything is excess can be toxic, even water. Seriously, don't even go there. The strengths up to 10% nicotine (100 mg/ml) are perfectly safe to handle at home. Many of us have been doing it for years successfully. You just have to be careful--measure and label everything accurately, that's key, and pay attention to what you're doing. Start with 12 mg/ml. If it's still not enough, try the 18 mg/ml. Or mix 12 and 18 (1:1) to make 15 mg/ml. Try them all. Go slowly. Always start low and increase your nicotine strength as needed. I don' t think you'll even need to go to 24 mg, but who knows. ALso, keep in mind that the equipment you're using matters. If you're an MTL (mouth-to-lung, low wattage) vaper, you'll need higher nic strength. Direct lung and high wattage--lower your nic. And forget about pure nic and anything higher then 10% nicotine bases. Those are NOT for DIY-ers. There's a very good reason ECF rules don't even allow discussing them here.