Yes, it is true that placebo is better than opioids at treating acute back and neck pain. A landmark trial published in The Lancet found that opioid therapy offered no more relief for acute back/neck pain or functional improvement than placebo.
The study involved more than 340 patients suffering from low back or neck pain, and the results showed that there was no difference in pain severity after six weeks between those who received opioids versus a placebo sugar pill. The mean pain score at 6 weeks was 2.78 in the opioid group, vs 2.25 in the placebo group.
Another study published in The Lancet found that supporting efficacy data for opioid analgesics in acute low back pain and neck pain are scarce. Therefore, it is generally advised to start off with everyday remedies like over-the-counter anti-inflammatories, and alternatives like heat therapy, massage, or exercise.