Is Britain more reliant on the US than the EU?

There's a lot of arguing over the exact deal Britain will have after leaving the EU but could this be less cause for concern than another international relationship?

You wouldn't believe how reliant the NHS is on medical devices and pharmaceuticals from American companies. If Britain made efforts to sever certain economic and diplomatic ties to the US then American medical companies could, at very short notice, withdraw from the UK market. This means that many medical devices, spare parts for medical devices, pharmaceuticals, and technical support and services will become unobtainable to British customers including the NHS.

In other words, the NHS could collapse as a result but it (probably) won't collapse as a result of Britain leaving the EU.