My bp for years has been 126/70 recently jumped to 165/70 i have been on atenolol 50mg for 7 years can it loose it's effectiveness?

Increased BP: You should check with your physician (p). Your dose of atenolol is low and with a sudden increase of bp, you will need more and another drug. A thing to consider is a renal artery stenosis that developed due to a atheroslcerotic plaque on one of your renal arteries. See you doctor, or a nephrologist, for more help with your question.

Possible: Atenolol is different from other beta blocker (bb) drugs in its class due to its water solubility. As you age, the % of relative body water decreases. But this has not clearly been shown to reduce its effectiveness in lowering BP in the elderly. Bbs are not great BP controlling meds anyway. I would echo the prior answer. More likely for the BP to get worse over time. You may need a new drug.